Natural gas is obtained from underground reservoirs and pumped through pipelines to various industrial and commercial consumers. Much of the natural gas is utilized for heating purposes and, accordingly, requires a BTU content of only 900 to 1000 BTU per m.c.f. A natural gas stream composed mainly of methane and ethane is sufficient to achieve such heating values. However, much of the natural gas obtained from underground reservoirs is rich in other components, such as propane, pentane and butane, which are heavier than methane. These components are industrially valuable in many processes, and, accordingly, separation of them from the methane and ethane prior to burning of the natural gas is highly desirable. Separation is usually accomplished at cryogenic temperature with distillation to separate and return methane and ethane to the gas pipeline while retaining a significant percentage of the propane and heavier components.